Solid oxide fuel cell

ABSTRACT

A solid oxide fuel cell includes a cathode, and an anode, and a solid electrolyte layer disposed between the cathode and the anode. The cathode includes a complex oxide having a perovskite structure expressed by the general formula ABO 3 . A standard deviation value for the atomic percentage of respective elements at the A site measured using energy dispersive X-ray spectroscopy at 10 spots in a single field on the sectional surface of the cathode is no more than 10.4.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/JP2012/082357, filed Dec. 13, 2012, which claimspriority to Japanese Patent Application No. 2011-277507 filed in Japanon Dec. 19, 2011, Japanese Patent Application No. 2012-033102 filed inJapan on Feb. 17, 2011, and International Application No.PCT/JP2012/073682, filed Sep. 14, 2012, the contents of each of whichare hereby incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a solid oxide fuel cell.

2. Background Information

In recent years, several materials and structures have been proposed inrelation to fuel cell batteries due to the attention focused on fuelcell batteries in light of effective use of energy resources andenvironmental problems.

JPA-2006-32132 discloses the use of an LSCF powder as a raw materialpowder for the cathode of a solid oxide fuel cell (SOFC).

SUMMARY

However, the available voltage may be reduced during repeated powergeneration using the fuel cell. The present inventors gained insightthat one cause of this reduction in output is deterioration of thecathode.

The technique disclosed herein is based on this insight and addressesthe problem of providing a solid oxide fuel cell that inhibitsdeterioration of a cathode.

The present invention solves the above problem and as a realizes thatthe deterioration of a cathode can be suppressed by increasing theuniformity of the concentration of the cathode components.

In that context, the solid oxide fuel cell disclosed herein includes acathode, an anode and a solid electrolyte disposed between the cathodeand the anode. The cathode contains a complex oxide having a perovskitestructure expressed by the general formula ABO₃. The standard deviationvalue of the atomic percentage of each element in the A site measured atthe sectional surface of the cathode using energy dispersive X-rayspectroscopy at 10 spots in a single field is no more than 10.4.

The technique disclosed herein provides a solid oxide fuel cell thatenables suppression of deterioration of a cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a flowchart describing a method of manufacturing an electrodematerial using a solid-phase method;

FIG. 2 is a flowchart describing a method of manufacturing an electrodematerial using a liquid-phase method;

FIG. 3 is a sectional view illustrating the principal features ofconfiguration of a vertically-striped fuel cell;

FIG. 4 is a SEM image of a single field and an image of concentrationmapping in relation to a sample No. 1 according to the example;

FIG. 5 is a SEM image of a single field and an image of concentrationmapping in relation to a sample No. 7 according to the examples;

FIG. 6 is a perspective view illustrating the external appearance of asegmented-in-series fuel cell; and

FIG. 7 is a sectional view along the direction I-I of the arrow in FIG.6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 1. Electrode Material

The electrode material includes a complex oxide having a perovskitestructure. The electrode material may include components other than acomplex oxide. As described below, the electrode material according tothe present embodiment is suitably used as a material to configure thecathode of the solid oxide fuel cell.

The composition of the complex oxide is expressed by the general formulaABO₃. Furthermore, at least one of La and Sr may be contained in the Asite. An actual example of this type of complex oxide for use as acathode material includes LSCF, that is to say, (La, Sr)(Co, Fe)O₃, LSFthat is to say, (La, Sr)FeO₃, LSC that is to say, (La, Sr)CoO₃, LNF thatis to say, La(Ni, Fe)O₃, SSC that is to say, (Sm, Sr)CoO₃, and the like.These complex oxides are materials that combine characteristics relatedto oxygen ion conductivity and electron conductivity, and are termedmixed conducting materials.

The electrode material may include the complex oxide as a “principalcomponent”. The feature “include as a principal component” when acomposition X contains a material Y means that the material Y comprisespreferably at least 60 wt % overall of composition X, more preferably 70wt %, and still more preferably at least 90 wt % of the overallcomposition X.

Furthermore, the electrode material may be configured as a powder (forexample, with an average particle diameter of about 1 micrometer to 5micrometers) or a disintegrated product (for example, with an averageparticle diameter of about 5 micrometers to 500 micrometers), or may bea agglomerate that is larger than the disintegrated product.

The electrode material preferably includes a highly uniform compositiondistribution. More specifically, a value of the standard deviation forthe atomic percentage of respective elements contained at the A site areacquired by use of energy dispersive X-ray spectroscopy (EDS) at 10spots in an arbitrary field in the electrode material is preferably nomore than 10.3. Furthermore, the atomic percentage of the respectiveelements contained at the B site is acquired, and when the standarddeviation of the atomic percentage is calculated, the standard deviationat the B site is preferably no more than 5.03.

For example, it is assumed that n types of elements A1, A2, A3, . . . Anare contained at the A site. When the value of the standard deviationfor the atomic percentage of the respective elements is acquired withreference to the atomic percentage obtained at 10 spots, if the value ofthe standard deviation for the atomic percentage for the element A1 islarger than the respective values for the standard deviation of theelements A2-An, it is preferred that the value of the standard deviationof the element A1 is no more than 10.3.

The arbitrary field as used herein is suitably within a range observedby an electron microscope such as an electron probe micro analyzer(EPMA) or a scanning electron microscope (SEM), or the like with amagnification of 100 times to 5000 times. The analysis spot size of therespective 10 spots may be no more than 1 micrometer. When thedistribution of the atomic percentage as described below is evaluatedbased on an observation at an excessively small magnification of lessthan 100 times, there are difficulties associated with the determinationof the uniformity of the distribution of each element in the micro rangethat is the object of the present invention. On the other hand, when thedistribution of the atomic percentage is evaluated based on anobservation at an excessively large magnification that exceeds 5000times, there is an increased possibility that only a non-uniform regionor only a uniform region will be observed as a result of the narrowobservation range. As a result, as stated above, it is preferred thatthe magnification of the electron microscope is in the range of 100times to 5000 times.

The position of the 10 spots may be selected for example on the basis ofthe concentration level in 10 stages that are determined in response tothe distribution of the atomic percentages measured using an electronprobe micro analyzer (EPMA). The concentration level in the 10 stages ispreferably set with reference to substantially the entire range of thedistribution of the atomic percentages. For example, the concentrationlevel in the 10 stages can be set by creating 10 divisions in theinterval between the maximum value and the minimum value in thecharacteristic X-ray intensity in the arbitrary field.

The ideal unit lattice for the complex oxide having a perovskitestructure expressed by the general formula ABO₃ is in the shape of acube. An A element is disposed at the corner of the unit lattice, and aB element is disposed in the body center of the unit lattice. The oxygenelement is disposed at the face center of the unit lattice. In thepresent embodiment, the position of the corner of the unit lattice atwhich the A element is disposed is termed the “A site”, and the positionof the corner of the unit lattice at which the B element is disposed istermed the “B site”.

2. Method of Manufacturing Electrode Material

An example of a method of manufacturing the electrode material describedin “Section 1.” above will be described below.

More specifically, the method of manufacture includes acquisition of acomplex oxide compound having a perovskite structure.

The method of obtaining the complex oxide compound includes a solidphase method, a liquid phase method (citrate process, Pechini method,co-precipitation method) or the like.

A “solid phase method” refers to a method in which a mixture obtained bymixing a starting material (powder) including constituent elements at apredetermined ratio is fired, and then subjected to comminution toobtain the target material.

A “liquid phase method” is a method for obtaining a target material thatincludes the steps of dissolving a starting material includingconstituent elements into a solution, obtaining a precursor of thetarget material from the solution by precipitation or the like, and thenperforming drying, firing and comminution.

The sequence of steps will be described below making reference to thefigures in relation to a configuration in which the electrode materialis manufactured using a solid phase method, and a configuration in whichthe electrode material is manufactured using a liquid phase method.

2-1 Method of Manufacturing Electrode Materials Using Solid Phase Method

FIG. 1 is a flowchart describing a method of manufacturing an electrodematerial using a solid phase method.

Firstly, in a step S101, a starting material is prepared according tothe type of complex oxide. When manufacturing LSCF as a complex oxide,for example, La₂O₃, SrCO₃, Co₃O₄ and Fe₂O₃ are prepared. The averageparticle diameter of La₂O₃ may be 0.1 micrometer to 0.7 micrometer, theaverage particle diameter of SrCO₃ may be 0.1 micrometer to 0.5micrometer, the average particle diameter of Co₃O₄ may be 0.1 micrometerto 1.0 micrometer, and the average particle diameter of Fe₂O₃ may be 0.1micrometer to 0.8 micrometer. Furthermore, it is preferred that theparticle size distribution of the starting material is controlled. Morespecifically, it is desirable that coarse particles of greater than orequal to 20 micrometers are removed in advance by use of an airclassifier or the like. The removal of coarse particles is effective foruniformity when executing mixing and synthesizing in subsequent steps.

Next, in step S102, the starting materials are classified. Morespecifically, for example, the specific surface area of each startingmaterial is adjusted by classification using an air classifier orexample. When manufacturing LSCF as a complex oxide, the specificsurface area of La₂O₃ is adjusted to 1 m²/g to 5 m²/g, the specificsurface area of SrCO₃ is adjusted to 1 m²/g to 7 m²/g, the specificsurface area of Co₃O₄ is adjusted to 1 m²/g to 7 m²/g, and the specificsurface area of Fe₂O₃ is adjusted to 1 m²/g to 10 m²/g.

Next, in a step S103, the respective starting materials are mixed at apredetermined mixing ratio. In the present embodiment, the mixingprocess preferably includes the steps of weighing the respectivestarting materials at a predetermined mixing ratio and placing thematerials into a pot mill together with pebbles (for example,application is possible of the pebbles used in the manufacture ofzirconia or alumina), rotating the pot mill for a predetermined time (10hrs to 120 hrs) in a dry state and then introducing a predeterminedamount (weight ratio relative to the starting material of 50% to 200%)of solvent (for example, when using an aqueous solvent, ion-exchangedwater may be used, and when using a solvent-based material, acetone maybe used), and rotating the pot mill further for a predetermined time (10hr to 300 hr) in a wet state. When performing a uniform mixture ofrespective starting material powders using wet mixing, it is preferredto perform sufficient disintegration under suitable mixing conditions ofthe starting material powder using dry mixing. The pebbles preferablyhave a diameter of 0.5 mm to 5 mm, and are preferably adjusted to 0.5 to3 times the weight of the starting material powder.

In this mixing process, it is preferred to add a predetermined additiveto the respective starting materials. The additives are phosphorus (P),chrome (Cr), and boron (B). The added amount of P is preferably at least1 ppm to no more than 50 ppm in a weight ratio relative to the startingmaterials, and more preferably at least 1 ppm and no more than 30 ppm.The added amount of Cr is preferably at least 1 ppm to no more than 500ppm in a weight ratio relative to the starting materials, and morepreferably at least 1 ppm and no more than 100 ppm. The added amount ofB is preferably at least 1 ppm to no more than 50 ppm in a weight ratiorelative to the starting materials, and more preferably at least 1 ppmand no more than 10 ppm. The additives are preferably added as oxides.The additives have the function of creating a uniform dispersion andmixture in the constituent components. In addition to comminution of thestarting materials in a dry mix in the previous step, an importantfactor in the control (uniformity) of the composition distribution ofthe electrode material is the combination of a process of wet mixing inlater steps. The mixing ratio of each starting material whenmanufacturing LSCF as a complex oxide may be performed by adjusting thestarting material ratio of La₂O₃, SrCO₃, Co₃O₄ and Fe₂O₃ in accordancewith the composition of the complex oxide.

Next, in step S104, the electrode material is synthesized by firing ofthe starting materials mixed in the pot mill. The synthesis conditionsmay be suitably adjusted within a range of a synthesis temperature of900 degrees C. to 1400 degrees C. and a synthesis time of 1 to 30 hrs inan oxidizing atmosphere.

Next, in step S105, the electrode material in a synthesized agglomeratedconfiguration is subjected to comminution. More specifically, theaverage particle diameter of the electrode material is adjusted to 0.3micrometers to 1.2 micrometers by introducing the electrode materialwith pebbles (for example, application is possible of the pebbles usedin the manufacture of zirconia or alumina) into the pot mill androtating for a predetermined time (5 hrs to 20 hrs). Furthermore, priorto comminution, the electrode material in an agglomerated configurationmay be subjected to preparatory disintegration.

Next, in step S106, the electrode material after comminution isclassified. More specifically, the specific surface area of eachstarting material is adjusted by classification using an air classifieror the like. When manufacturing LSCF as a complex oxide, the specificsurface area is adjusted to 3 m²/g to 12 m²/g.

2-2 Method of Manufacture of Electrode Material using Liquid-PhaseMethod

FIG. 2 is a flowchart describing a method of manufacturing an electrodematerial using a liquid-phase method.

Firstly, in step S201, a starting material is prepared corresponding tothe type of complex oxide. When manufacturing LSCF as the complex oxideby use of a co-precipitation method or citrate method, La(NO₃)₃.6H₂O,Sr(NO₃)₂, Co(NO₃)₃.9H₂O and Fe(NO₃)₃.9H₂O are prepared. The averageparticle diameter of La(NO₃)₃.6H₂O may be 0.3 micrometers to 0.6micrometers, the average particle diameter of Sr(NO₃)₂ may be 0.1micrometers to 0.4 micrometers, the average particle diameter ofCo(NO₃)₃.9H₂O may be 0.2 micrometers to 0.5 micrometers, and the averageparticle diameter of Fe(NO₃)₃.9H₂O may be 0.3 micrometers to 0.8micrometers. When manufacturing LSCF using a Pechini method, La₂O₃,SrO₃, Co₃O₄ and Fe(NO₃)₃.9H₂O are prepared to have the above averageparticle diameter. Furthermore, controlling the particle sizedistribution of the starting materials is important. More specifically,it is desirable to remove coarse particles of greater than or equal to15 micrometers in advance by use of an air classifier. The removal ofcoarse particles is effective for uniformity when executing mixing andsynthesizing (calcinating) in subsequent steps.

Next, in step S202, the starting materials are classified. Morespecifically, for example, the specific surface area of each startingmaterial is adjusted by classification using an air classifier. Whenmanufacturing LSCF as a complex oxide by use of co-precipitation or acitrate method, the specific surface area of La(NO₃)₃.6H₂O is adjustedto 2 m²/g-8 m²/g, the specific surface area of Sr(NO₃)₂ is adjusted to 1m²/g-5 m²/g, the specific surface area of Co(NO₃)₃.9H₂O is adjusted to 2m²/g-5 m²/g, and the specific surface area of Fe(NO₃)₃.9H₂O is adjustedto 3 m²/g-10 m²/g.

Next, in a step S203, the respective starting materials are mixed at apredetermined mixing ratio. More specifically, when manufacturing LSCFby use of co-precipitation, after dissolving the starting materials in apure state to prepare a 0.2M aqueous solution, an aqueous nitratesolution is added while stirring in a precipitation agent. Whenpreparing the LSCF using a citrate method, the respective startingmaterials are dissolved in a pure state and citric acid is added untilall the metal is precipitated, and the viscosity is adjusted by use ofheating after immersion to approximately 60 degrees C. to dehydrate.When preparing LSCF using a Pechini method, after preparing an aqueousnitrate solution for each of the starting materials and mixing allsolutions, citric acid and ethylene glycol are added.

In this mixing process, it is preferred to add a predetermined additiveto the respective starting materials. The additives are phosphorus (P),chrome (Cr), and boron (B). The concentration of P contained in theadditive is preferably at least 1 ppm to no more than 50 ppm in a weightratio relative to the starting materials, and more preferably at least 1ppm and no more than 30 ppm. The concentration of Cr contained in theadditive is preferably at least 1 ppm to no more than 500 ppm in aweight ratio relative to the starting materials, and more preferably atleast 1 ppm and no more than 100 ppm. The concentration of B containedin the additive is preferably at least 1 ppm to no more than 50 ppm in aweight ratio relative to the starting materials, and more preferably atleast 1 ppm and no more than 10 ppm. The additives have the function ofcreating a uniform dispersion and mixture in the constituent components,or during thermal synthesis processes, and non-uniformity in each of theelements (for example, resulting from phase splitting, heterogeneousphase precipitation, or the like) can be inhibited as a result of theseadditives. As a result, uniformity of the composition distribution ofthe electrode material is enabled by suitable control of the addedamount of the additives.

Next, in step S204, the aqueous solution prepared in step S203 is dried.When using co-precipitation, vacuum drying is used at approximately 110degrees C., when using a citrate method, drying is performed atapproximately 70 degrees C., and when using a Pechini method, drying isperformed at approximately 200 degrees C.

Next, in step S205, the electrode material is synthesized by firing ofthe dried starting materials. The synthesis conditions are suitablyadjusted within a range of a synthesis temperature of 900 degrees C. to1400 degrees C. and a synthesis time of 1 to 30 hrs in an oxidizingatmosphere.

Next, in step S206, the electrode material that is in a configuration ofa synthesized agglomerate is subjected to comminution. In step S207, theelectrode material after comminution is classified. The details of thesesteps are the same as steps S105 and S106 described above.

3. Vertically-Striped Fuel Cell (Solid Oxide Fuel Cell)

A solid oxide fuel cell is an example of a fuel cell. In particular, aSOFC will be mainly described that has a cell stack structure in which aplurality of fuel cells are stacked.

3.1 Overview of Fuel cell

As illustrated in FIG. 3, the fuel cell 10 includes a fuel cell(hereinafter simply referred to as “cell”) 1, and a current collectingmember 4.

3-2 Overview of Cell 1

The cell 1 is a thin ceramic plate. The thickness of the cell 1 is forexample 30 micrometers to 700 micrometers, and the diameter of the cell1 is for example 5 mm to 50 mm. The cell 1 as illustrated in FIG. 3includes an anode 11, a barrier layer 13, a cathode 14, and anelectrolyte layer 15 (solid electrolyte layer).

3-3 Anode

The material used in the anode 11 for example includes a material usedin the formation of the anode in a known fuel cell. More specifically,the material used in the anode 11 may include NiO—YSZ (nickeloxide-yttria-stabilized zirconia) and/or NiO—Y₂O₃ (nickel oxide-yttria).The anode 11 may include these materials as a main component. The anode11 functions as the anode.

Furthermore, the anode 11 may function as a base plate that supports theother layers included in the cell 1 (in other words, a support body).That is to say, the thickness of the anode 11 may have the maximumthickness of the plurality of layers contained in the cell 1. Morespecifically, the thickness of the anode 11 is of the order of 10micrometers to 600 micrometers.

The anode 11 can be imparted with conductive properties by applicationof a reduction treatment (for example, a treatment of reducing NiO toNi).

The anode 11 may include at least two layers. For example, the anode 11may have two layers, that is to say, a base plate and an anode-activelayer (fuel-side electrode) formed thereon. The material in the baseplate is configured by a material that includes properties such aselectron conductivity. The anode-active layer is configured by amaterial that includes properties such as electron conductivity andproperties such as oxidizing ion (oxygen ion) conductivity. The“proportion of the volume of material that has oxidizing ion (oxygenion) conductivity relative to the total volume excluding the pores” inthe anode active layer is greater than the “proportion of the volume ofmaterial that has oxidizing ion (oxygen ion) conductivity relative tothe total volume excluding the pores” in the base plate. The material inthe base plate and the anode active layer can be selected from thematerials for the anode 11 described above. More specifically, acombination is possible of a base plate configured from NiO—Y₂O₃ and theanode active layer configured by NiO—YSZ.

3-4 Barrier Layer

The barrier layer 13 is provided between the cathode 14 and the anode11, and more specifically, is provided between the cathode 14 and theelectrolyte layer 15.

The barrier layer 13 includes cerium. The barrier layer may includecerium as the ceria (cerium oxide). More specifically, materials thatare used in the barrier layer 13 include ceria and ceria-based materialsincluding rare-earth metal oxides configured as a solid solution inceria. The barrier layer 13 may include a ceria-based material as a maincomponent.

More specifically, the ceria-based material includes GDC ((Ce, Gd)O₂:gadolinium doped ceria), and SDC ((Ce, Sm)O₂: samarium doped ceria). Theconcentration of the rare earth metal in the ceria-based material ispreferably 5 to 20 mol %. The barrier layer 13 may include an additivein addition to a ceria-based material.

The thickness of the barrier layer 13 is no more than 30 micrometers.

The barrier layer 13 suppresses the diffusion of cations from thecathode 14 into the electrolyte layer 15. As a result, the barrier layer13 enables suppression of a reduction in the output density, andincreases the product life of the cell 1.

3-5 Cathode

The cathode 14 contains a complex oxide having a perovskite structureexpressed by the general formula ABO₃. This type of complex oxide ispreferably the electrode material that was described in Section 1 above.More specifically, the complex oxide includes LSCF, LSF, LSC, LNF, SSC,or the like. The cathode 14 may include components other than the abovetypes of complex oxide. For example, the cathode 14 may be configured asa composite with the material (ceria or zirconia, or the like) of theelectrolyte layer 15 described below.

As used herein the composition distribution of the cathode 14 ispreferably exhibits a highly uniform configuration. More specifically,in an arbitrary field on a sectional surface of the cathode 14, therespective atomic percentages of each element contained at the A site isacquired using EDS at 10 spots, and when the standard deviation of theatomic percentage is calculated, it is preferred that the standarddeviation value of the A site is no more than 10.4. For example, it isassumed that n types of elements A1, A2, A3, . . . An are present at theA site. When the standard deviation value of the atomic percentage ofeach element is acquired based on the atomic percentage obtained at 10spots, it is preferred that the standard deviation value of the atomicpercentage of element A1, and the standard deviation value of the atomicpercentage of the element A1 when larger than the standard deviationvalue respectively of A2 to An is no more than 10.4.

However, when the cathode 14 contains a component other than the complexoxide, the standard deviation of the atomic percentage of the elementscontained at the A site of the complex oxide may be more no more than10.4. Therefore, when the cathode 14 is configured from a composite ofthe material of the electrolyte layer 15 and the complex oxide, only thecomplex oxide that is present on the sectional surface of the cathode 14may be selected and observed.

An arbitrary field may be defined as the range that can be observed at amagnification of 100× to 5000× when using an electron microscope such asan SEM, EPMA, or the like. The analysis spot size of the respective 10spots may have a configuration of less than or equal to 1 micron.Furthermore, the position of the 10 spots may be selected in response tothe concentration level of the 10 stages for example set based on thedistribution of the atomic percentage measured using EPMA. In otherwords, the concentration level in the 10 stages may be set by dividinginto 10 the interval between the maximum value and the minimum value ofthe specific X-ray intensity in an arbitrary field.

The cathode 14 is preferably includes an additive (P, Cr, and B) at apredetermined weight ratio relative to the total weight of the electrodematerial. In this configuration, the content amount of P is preferablyat least 1 ppm to no more than 50 ppm in a weight ratio relative to thestarting materials, and more preferably at least 1 ppm and no more than30 ppm. The content amount of Cr is preferably at least 1 ppm to no morethan 500 ppm in a weight ratio relative to the starting materials, andmore preferably at least 1 ppm and no more than 100 ppm. The contentamount of B is preferably at least 1 ppm to no more than 50 ppm in aweight ratio relative to the starting materials, and more preferably atleast 1 ppm and no more than 10 ppm.

The cathode 14 may include additives other than P, Cr and B, and forexample, the cathode 14 may include trace amounts of Na, Mg, Al, Si, Ca,Sc, Ti, Ni, Zn, Y, Zr, Ba, Ce, Gd, or the like.

The thickness of the cathode 14 may be of the order of 5 micrometers to50 micrometers.

3-6 Electrolyte Layer

The electrolyte layer 15 is provided between the barrier layer 13 andthe anode 11.

The electrolyte layer 15 includes zirconium. The electrolyte layer 15may include zirconium in the form of zirconia (ZrO₂). More specifically,the electrolyte layer 15 may include zirconia as a main component. Theelectrolyte layer 15 may include an additive such as Y₂O₃ and/or Sc₂O₃in addition to zirconia. These additives may function as a stabilizer.The added amount of the additive in the electrolyte layer 15 is of theorder of 3 to 20 mol %. In other words, the material used in theelectrolyte layer 15 includes yttria-stabilized zirconia such as 3YSZ,8YSZ, and 10YSZ or zirconia-based materials such as ScSZ(scandia-stablized zirconia).

The thickness of the electrolyte layer 15 may be no more than 30micrometers.

3-7 Current Collecting Member

A current collecting member 4 includes a plurality of conductiveconnection portions 41.

As illustrated in FIG. 3, the conductive connection portions 41 areconfigured as a depressed portion provided in the current collectingmember 4, and the bottom portion thereof is connected through aconductive adhesive 411 to the cathode 14. The bottom portion of theconductive connection portions 411 includes a periphery and anon-connected position.

During power generation, fuel gas is supplied to the anode 11. Thesupply of air to the cathode 14 draws air from the side surface of thecell stack structure (for example, the front of the face of the page inFIG. 3).

Although this is not shown, the fuel cell 10 further includes a membersuch as a lead that sends a current generated by the cell stack to anexternal apparatus, and a gas reforming unit that includes a catalyst orthe like for reforming the fuel gas.

4. Method of Manufacturing Fuel Cell 4-1 Formation of Anode

The anode 11 can be formed by powder compaction. That is to say, theanode 11 may include the feature of introducing powder, in whichmaterial for the anode 11 is mixed, into a mold, and compressing tothereby mold a compacted powder body.

The material for the anode 11 may be configured according to thedescription above in relation to the configuration of the fuel cell. Thematerial includes use of nickel oxide, zirconia and a pore forming agentas required. A pore forming agent is an additive that forms pores in theanode. The pore forming agent includes use of a material that is removedin later processing steps. Examples of such materials include cellulosepowder.

This is no particular limitation on the mixing ratio of the material,and the mixing ratio may be suitably set in response to thecharacteristics or the like required by the fuel cell.

The pressure applied to the powder during powder compaction molding isset to impart sufficient rigidity to the anode.

The internal structure of the anode 11 such as the gas conduit (notshown) is formed by powder compaction molding in a configuration inwhich a member that is removed by firing (a cellulose sheet or the like)is disposed in an inner portion of the powder body and then firing isperformed.

4-2 Formation of Electrolyte Layer

The method of manufacturing the fuel cell includes formation of theelectrolyte layer on a molded body of the anode formed by powdercompaction.

The method of formation of the electrolyte is a method such as CIP (coldisostatic pressing) that uses an electrolyte material that is processedinto a sheet configuration, or thermo-compression bonding. Otherwise, aslurry dip method may be used in which the anode is immersed into anelectrolyte material adjusted to a slurry configuration. When using theCIP method, the pressure during the pressing operation on the sheet ispreferably 50 to 300 MPa.

4-3 Firing

The method of manufacturing the fuel cell includes co-firing(co-sintering) of the electrolyte layer and the anode formed by powdercompaction. The temperature and the time for firing are set in responseto the cell material.

4-4 Degreasing

Degreasing may be performed prior to firing in 4-3. The degreasing isexecuted by heating. The conditions such as temperature and time are setin response to the material of the cell or the like.

4-5 Formation of Cathode

The cathode is formed by firing after formation of a layer of materialfor the cathode by a printing method, powder compaction or the like on astacked body of the barrier layer, the electrolyte layer and the anode.More specifically, in case of an electrode material configured fromLSCF, when using a printing method, a paste prepared by mixing LSCFtogether with a binder, dispersal agent and dispersal medium is printedonto the stacked body and fired (firing temperature 900 degrees C. to1100 degrees C., and firing time 1 hr to 10 hrs).

4-6 Other Processing Steps

Other steps may be included in the manufacturing method depending on theconfiguration of the fuel cell. For example, the manufacturing methodmay include a step of providing a reaction prevention layer between theelectrolyte layer and the cathode, or may include a step of forming adouble layered structure in the anode (a step of forming the base plateand a step of forming the anode active layer).

5. Segmented-in-series Fuel Cell

The fuel cell 10 described above includes a plurality of stacked cells 1and a current collecting member 4 connecting the cells 1 electrically.In other words, the fuel cell 10 is a vertically-striped fuel cell.However, the technique disclosed herein may also be applied to asegmented-in-series fuel cell. A segmented-in-series fuel cell will bedescribed below.

The segmented-in-series fuel cell (hereinafter simply referred to as a“fuel cell”) 100 includes a support base plate 102, an anode 103, anelectrolyte layer 104, a cathode 106, an interconnector 107, a currentcollecting unit 108, and a barrier layer 13. The fuel cell 100 includesa plurality of cells 110. Those component elements that are the same asthe component elements already described above are denoted by the samereference numerals, and such description will not be repeated. In FIG.6, for sake of convenience of description, the current collecting unit108 is not illustrated.

The fuel cell 100 includes the cells 110 disposed on the support baseplate 102 and an interconnector 107 that electrically connects the cells110. The cells 110 are units that include an anode 103 and a cathode 106that corresponds to the anode 103. More specifically, the cells 110include an anode 103, an electrolyte layer 104 and a cathode 106 stackedin the thickness direction (y axis direction) of the support base plate102. The anode 103, the electrolyte layer 104 and the cathode 106configure the power generation element of the cell 110.

The support base plate 102 is flat and elongated in one direction (zaxis direction). The support base plate 102 is a porous body that haselectrical insulating properties. The support base plate 102 may includenickel. More specifically, the support base plate 102 may containNi—Y₂O₃ (nickel yttria) as a main component. The nickel may be includedas an oxide (NiO). During power generation, NiO may be reduced to Ni byhydrogen gas.

As illustrated in FIG. 6 and FIG. 7, a conduit 123 is provided in aninner portion of the support base plate 102. The conduit 123 extendsalong the longitudinal direction (z axis direction) of the support baseplate 102. During power generation, fuel gas flows into the conduit 123,through a hole that is provided in the support base plate 102 to therebysupply fuel gas to the anode 103 described below.

The anode 103 is provided on the support base plate 102. A plurality ofanodes 103 is disposed on a single support base plate 102 and isarranged in the longitudinal direction (z axial direction) of thesupport base plate 102. That is to say, a space is provided betweenadjacent anodes 103 with respect to the longitudinal direction (z axisdirection) of the support base plate 102.

The composition of the anode 103 may be the same as the composition ofthe anode 11.

The anode 103 may include an anode current collecting layer and an anodeactive layer. The anode current collecting layer is provided on thesupport base plate 102, and the anode active layer is provided on theanode current collecting layer while avoiding superimposition withrespect to the interconnector 107.

The anode 103 may include an anode current collecting layer and an anodeactive layer. The anode current collecting layer is provided on thesupport base plate 102 and the anode active layer is provided on theanode current collecting layer. The composition of the anode currentcollecting layer and the anode active layer has been described above.

The electrolyte layer 104 is also termed a solid electrolyte layer. Asillustrated in FIG. 7, the electrolyte layer 104 is provided on theanode 103. In a region that is not provided with the anode 103 on thesupport base plate 102, the electrolyte layer 104 may be provided on thesupport base plate 102.

The electrolyte layer 104 includes a non-connected position in thelongitudinal direction (z axis direction) of the support base plate 102.In other words, a plurality of electrolyte layers 104 is disposed at aninterval in the z axis direction. Namely, a plurality of electrolytelayers 104 is provided along the longitudinal direction (z axisdirection) of a single support base plate 102.

Electrolyte layers 104 adjacent in the z axis direction are connected byan interconnector 107. In other words, the electrolyte layers 104 areconnected from an interconnector 107 to an interconnector 107 that isadjacent to that interconnector 107 in the longitudinal direction (zaxis direction) of the support base plate 102. The interconnector 107and the electrolyte layer 104 have a dense structure in comparison tothe support base plate 102 and the anode 103. Therefore, theinterconnector 107 and the electrolyte layer 104 function as a sealingportion that partitions air and fuel gas by the provision of a connectedstructure in the z axis direction in the fuel cell 100.

The composition of the electrolyte layer 104 may include a compositionthat is the same as the electrolyte layer 15 as described above.

The same description provided in relation to the vertical-striped fuelcell applies to the configuration of the barrier layer 13. The barrierlayer 13 is provided between the cathode 106 and the electrolyte layer104.

The cathode 106 is disposed on the barrier layer 13 without projectingfrom the outer edge of the barrier layer 13. One cathode 106 is stackedon one anode 103. That is to say, a plurality of cathodes 106 isprovided along the longitudinal direction (z axis direction) of thesupport base plate 102 on a single support base plate 102.

The cathode 106 is configured by a complex oxide having a perovskitestructure expressed by the general formula ABO₃ in the same manner asthe cathode 14 described above. The cathode 106 may include the complexoxide as a “principal component”, and may include components other thanthe complex oxide. The material used to configure the cathode 106 ispreferable the electrode described in “Section 1.”.

As used herein the composition distribution of the cathode 106 ispreferably exhibits a highly uniform configuration. More specifically,in an arbitrary field on a sectional surface of the cathode 106, therespective atomic percentages of each element contained at the A site isacquired using EDS at 10 spots, and when the standard deviation of theatomic percentage is calculated, it is preferred that the standarddeviation value of the A site is no more than 10.4. The position of the10 spots and the analysis spot size in an arbitrary field is asdescribed in “Section 1.”.

The cathode 106 preferably includes an additive (P, Cr, and B) at apredetermined weight ratio relative to the total weight of the electrodematerial in the same manner as the cathode 15 of the vertically-stripedfuel cell described above. In this configuration, the content amount ofP is preferably at least 1 ppm to no more than 50 ppm in a weight ratiorelative to the starting materials, and more preferably at least 1 ppmand no more than 30 ppm. The content amount of Cr is preferably at least1 ppm to no more than 500 ppm in a weight ratio relative to the startingmaterials, and more preferably at least 1 ppm and no more than 100 ppm.The content amount of B is preferably at least 1 ppm to no more than 50ppm in a weight ratio relative to the starting materials, and morepreferably at least 1 ppm and no more than 10 ppm.

As described above, the interconnector 107 may be disposed to configureelectrical contact between the cells 110. In FIG. 7, the interconnector107 is stacked onto the anode 103.

In the present specification, “stack” includes the disposition of twoelements in connection, and a disposition that provides an overlap inthe y axis direction although there is not a connection.

In FIG. 7, as described above, the interconnector 107 is disposed tospan the interval between the electrolyte layers 104 in the longitudinaldirection (z axis direction) of the support base plate 102. In thismanner, cells 110 that are adjacent in the longitudinal direction (zaxis direction) of the support base plate 102 are electricallyconnected.

The interconnector 107 configures an electrode that is used for theelectrical connection between the plurality of cells 110. Morespecifically, the interconnector 107 illustrated in FIG. 7 functions asan electrode for the cells 110 disposed on the right side of FIG. 7.

The interconnector 107 that configures the electrode as described above,in the same manner as the cathode 106 described above, includes a maincomponent of a perovskite complex oxide as a main component. Inparticular, a chromite-based material such as lanthanum chromite(LaCrO₃) is an example of a perovskite complex oxide used in theinterconnector 107.

The composition formula for the lanthanum chromite is expressed bygeneral formula (1) below.

Ln_(1-x)A_(x)Cr_(1-y-z)B_(y)O₃  (1)

In Formula (1), wherein Ln is at least one type of element selected fromthe group of Y and a lanthanoid, A is at least one type of elementselected from the group of Ca, Sr and Ba, and B is at least one type ofelement selected from the group of Ti, V, Mn, Fe, Co, Cu, Ni, Zn, Mg andAl, and wherein 0.025≦x≦0.3, 0≦y≦0.22, 0≦z≦0.15.

Lanthanum chromite is a material that can stably exist under both anatmospheric and reducing atmosphere at the operating temperature (600 to1000 degrees C.) of the SOFC, and is preferably used as aninterconnector material (electrode material) of an SOFC cell thatincludes horizontal stripes.

However, it is known that lanthanum chromite is a sintering resistantmaterial, and addition is required of an additive that facilitatesfiring, such as a sintering agent (CaO, SrO, or the like), to co-sinterwith the support base plate 102, the anode 103 and the electrolyte layer104 for application to the SOFC cell.

The current collecting unit 108 is disposed to electrically connect theinterconnector 107 and the cell 110. More specifically, the currentcollecting unit 108 is provides a connection from the cathode 106 to theinterconnector 107 that is included in the cell 110 that is adjacent tothe cell 110 that includes the cathode 106. The current collecting unit108 may include conductive properties.

The cathode 106 that is included in the cell 110 is electricallyconnected to the anode 103 of the adjacent cell 110 through the currentcollecting unit 108 and the interconnector 107. That is to say, thecurrent collecting unit 108 participates in the connection between cells110 in addition to the interconnector 107.

The specific dimensions of each component of the fuel cell 100 may beset as shown below.

Width W1 of support base plate 102: 1 to 10 cm

Thickness W2 of support base plate 102: 1 to 10 mm

Length W3 of support base plate 102: 5 to 50 cm

Distance W4 from outer surface of support base plate 102 (interfacebetween support base plate 102 and anode) to conduit 123: 0.1-4 mm

Thickness of Anode 103: 50-500 micrometers (When the anode 103 includesan anode current collecting layer and an anode active layer: thicknessof anode current collecting layer: 50-500 micrometers, thickness ofanode active layer: 5-30 micrometers)

Thickness of electrolyte layer 104: 3-50 micrometers

Thickness of cathode 106: 10-100 micrometers

Thickness of interconnector 107: 10-100 micrometers

Thickness of current collecting unit 108: 50-500 micrometers

The dimensions described in relation to a vertically-striped fuel cellmay be adopted for the constituent elements that are not specificallydisclosed. However it goes without saying that the technique hereindisclosed is not limited to these values.

(Additional Note)

The solid oxide fuel cell includes a cathode, an anode and a solidelectrolyte disposed between the cathode and the anode, the cathodeincluding a complex oxide material that has a perovskite structureexpressed by the general formula ABO₃. The complex oxide is preferablysuch that P is at least 1 ppm and no more than 50 ppm, Cr is at least 1ppm and no more than 500 ppm, and B is at least 1 ppm and no more than50 ppm in a weight ratio relative to the total weight of the complexoxide.

The content amount of P included in the cathode is more preferably nomore than 30 ppm in a weight ratio relative to the total weight of thecathode.

The content amount of Cr included in the cathode is more preferably nomore than 100 ppm in a weight ratio relative to the total weight of thecathode.

The content amount of B included in the cathode is more preferably nomore than 10 ppm in a weight ratio relative to the total weight of thecathode.

Examples A. Preparation of Cell

A NiO-8YSZ anode active layer (10 micrometers), an 8YSZ electrolytelayer (3 micrometers) and a GDC barrier layer (3 micrometers) arestacked on an NiO-8YSZ anode base plate (500 micrometers), and firedunder conditions of 1400 degrees C. for 2 hours.

As illustrated in Table 1 to Table 3, 10 types of electrode materials(No. 1 to No. 10) including (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃, 6types of electrode materials (No. 11 to No. 16) including(La_(0.8)Sr_(0.2))FeO₃ as shown in Table 7 to Table 9, and 6 types ofelectrode materials (No. 17 to No. 22) including (Ni_(0.6)Fe_(0.4))O₃ asshown in Table 13 to Table 15 were obtained. Then as illustrated inTable 19, 6 types of electrode materials (No. 23 to No. 28) including(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ in the same manner as No. 1 toNo. 10 were obtained. However, no additives were actively added to No.28. ICP analysis is used to confirm that the added amount of theadditive (at least one of P, Cr and B) during electrode operationcorresponds to the content amount of the additive in the electrodematerial after calcination (synthesis).

Those electrode materials that are expressed using the same generalformula but denoted by different reference numerals differ in relationto starting materials, firing conditions, or comminution conditions.Furthermore, the tables indicate whether each electrode material wassynthesized using a solid phase method or a liquid phase method.Furthermore, the content amount of the additive (P, Cr or B) included inthe electrode material is disclosed in the table.

The average particle diameter of the resulting disintegrated product is200 micrometers. The disintegrated product was used in the measurementof the composition distribution described below.

The disintegrated product was subjected to comminution using a ball millapparatus. The average particle diameter of the electrode material(powder) was all no more than 1.0 micrometer upon measurement using alaser diffraction/scattering type particle size distribution measurementapparatus (LA-700 manufactured by Horiba Ltd.).

A paste was prepared using the resulting powder and the paste was usedto form a film with a screen printing method resulting in a cathode (30micrometers) on the barrier layer. The cathode was attached by firingonto the barrier layer by heating to no more than 1000 degrees C. for 2hours.

SOFCs were obtained in the above manner.

B. Evaluation B-1 Measurement of Composition Distribution of ElectrodeMaterial

The atomic percentage distribution of each element in the disintegratedproduct formed of electrode material according to No. 1 to No. 22 wasmeasured using EPMA. More specifically, measurements are performingusing an electron probe micro analyzer manufactured by JEOL Ltd. (model:DCA-8500F). Next, in an arbitrary field, EDS is used to measure theatomic percentage (mol %) of an oxide of each element at the A site andeach element at the B site in relation to 10 spots in a section notforming a cavity that can be identified in an SEM image. Morespecifically, measurements were performed using a field emissionscanning electron microscope (model: ULTRA55) manufactured by Zeiss AG(Germany).

Then, the respective concentration of La and Sr at the A site wasmeasured at 10 spots in relation to each of the samples No. 1 to No. 10to obtain an average value for the La concentration and the standarddeviation of the La concentration at each spot and the average value forthe Sr concentration and the standard deviation of the Sr concentrationat each spot. In the same manner a concentration average value and astandard deviation for the concentration at each spot were obtained forCo and Fe at the B site. Furthermore, the maximum value of the standarddeviation in relation to the atomic percentage of elements at the A siteand the maximum value of the standard deviation in relation to theatomic percentage of elements at the B site were obtained for eachsample No. 1 to No. 10.

The same operation was performed in relation to the concentration of Feat the B site and La and Sr at the A site for each sample No. 11 to No.16, and the same operation was performed in relation to theconcentration of Fe and Ni at the B site and La at the A site for eachsample No. 17 to No. 22.

B-2 Measurement of Composition Distribution of Cathode

The atomic percentage distribution of each element was measured using anEPMA (JEOL Ltd. model: DCA-8500F) on a sectional surface of the cathodeformed from the cathode material according to No. 1 to No. 22. Next, theatomic percentage (mol %) as an oxide of each element in the A site andthe B site in 10 spots in the SEM image in an arbitrary field wasmeasured using EDS (model: ULTRA55, manufactured by Zeiss AG (Germany)on a sectional surface of the cathode.

More specifically, the respective concentration of La and Sr at the Asite on a sectional surface of the cathode formed from the cathodematerial according to No. 1 to No. 10 was measured at 10 spots tothereby obtain a standard deviation of the concentration at each spotand the average value of the Sr concentration in addition to thestandard deviation of the concentration at each spot and the averagevalue of the La concentration. Furthermore, the standard deviation ofthe concentration at each spot and the concentration average value wasobtained in the same manner in relation to Co and Fe at the B site. Themaximum value of the standard deviation at the atomic percentage of eachelement at the A site and maximum value of the standard deviation of theatomic percentage of each element at the B site were obtained inrelation to each sample according to No. 1 to No. 10.

The same operation was performed in relation to the concentration of Feat the B site and La and Sr at the A site on the sectional surface ofthe cathode according to No. 11 and No. 16, and the same operation wasperformed in relation to the concentration of Fe and Ni at the B siteand La at the A site on the sectional surface of the cathode accordingto No. 17 and No. 22.

B-3 Durability Experiments

Continuous power generation was performed using the prepared SOFC cell.The voltage drop rate (deterioration rate) was calculated per 1000 hoursusing power generation conditions of 750 degrees C. and current density:0.3 A/cm². A deterioration rate of no more than 1% was evaluated as“good”.

C Results

C-1 No. 1 to No. 10: (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃

In relation to the samples No. 1 to No. 10, the measurement results forthe concentration of No. 1 sample as an example and the results of thecalculation of the average value and the standard deviation are shown inTable 1. Table 2 shows the maximum value of the standard deviation forthe atomic percentage of each element in relation to samples No. 1 toNo. 10. The maximum value of the standard deviation at the A site andthe maximum value of the standard deviation at the B site are underlinedin relation to each sample. Table 3 shows the maximum value of thestandard deviation at the A site and the maximum value of the standarddeviation at the B site shown in Table 2, the voltage drop rate(deterioration rate) per 1000 hours, and the evaluation result based onthe voltage drop rate for samples No. 1 to No. 10.

FIG. 4 and FIG. 5 show respective SEM images and concentration mappingimages for the same field in relation to samples No. 1 and No. 7. InFIG. 4 and FIG. 5, the actual positions of high atomic percentage areshown by a red color and positions of low atomic percentage are shownwith a blue color.

Furthermore, Table 4 shows the measurement results for the concentrationand the results of the calculation of the average value and the standarddeviation on the sectional surface of the cathode according to sampleNo. 1 of samples No. 1 to No. 10. Table 5 shows the maximum value of thestandard deviation of the atomic percentage of each element in thecathode according to No. 1 to No. 10. In Table 5, an underline isapplied to the maximum value of the standard deviation at the B site andthe maximum value of the standard deviation at the A site. Table 6 showsthe evaluation results based on the voltage drop rate (deteriorationrate) per 1000 hours, and the maximum value of the standard deviation atthe B site and the maximum value of the standard deviation at the A siteshown in Table 5 in relation to the cathode according to No. 1 to No.10.

TABLE 1 Concentration Analysis Results for 10 Spots in Sample No. 1 of(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ Analysis Spot La (mol %) Sr (mol%) Co (mol %) Fe (mol %) 1 17.1 30.9 6.9 45.1 2 19.4 28.7 6.5 45.4 324.4 22.3 7.9 45.4 4 24.1 22.5 8.6 44.8 5 22.1 28.8 7.7 42.1 6 29.7 20.19.1 41.1 7 32.5 22.5 10.3 34.7 8 38.3 16.8 9.5 35.4 9 25.6 20.3 10.443.7 10  19.5 26.8 7.3 46.4 Average Value 25.27 23.97 8.35 42.41Standard 6.23 4.34 1.36 3.99 Deviation

TABLE 2 Maximum Value for Standard Deviation and Additive Content Amountfor Samples No. 1 to No. 10 of (La_(0.6)Sr_(0.4)) (Co_(0.2)Fe_(0.8))O₃Additive Standard Deviation content Sample Synthesis A site B siteamount (ppm) No. Method La Sr Co Fe P Cr B 1 Solid phase 6.23 4.34 1.363.99 40 400 30 method 2 Solid phase 3.12 4.11 0.82 1.54 35 300 20 method3 Solid phase 10.3  8.32 2.87 3.61 50 500 50 method 4 Solid phase 1.560.89 0.68 0.56 40 250 20 method 5 Solid phase 7.52 13.2  4.98 2.86 70800 80 method 6 Solid phase 11.5  6.32 3.15 4.88 60 630 60 method 7Liquid phase 0.05 0.04 0.1  0.05 20 20 3 method 8 Liquid phase 0.27 0.460   0.07 30 100 5 method 9 Liquid phase 1.13 1.03 0.68 0.36 45 460 50method 10 Liquid phase 0.2  0.25 0.03 0.05 20 60 10 method

TABLE 3 Evaluation Result for Deterioration Rate and Maximum Value ofStandard Deviation in Samples No. 1 to No. 10 of(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ Maximum Value Maximum ValueStandard Standard Deterioration Sample Deviation at A Deviation at BRate Evaluation No. site site (%/1000 hr) Result 1 6.23 3.99 0.76 Good 24.11 1.54 0.63 Good 3 10.3 3.61 0.95 Good 4 1.56 0.68 0.65 Good 5 13.24.98 1.85 Poor 6 11.5 4.88 1.52 Poor 7 0.05 0.10 0.30 Good 8 0.46 0.070.52 Good 9 1.13 0.68 0.87 Good 10 0.25 0.05 0.45 Good

TABLE 4 Concentration Analysis Result for 10 Spots on Cathode configuredfrom Sample No. 1 of (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ AnalysisSpot La (mol %) Sr (mol %) Co (mol %) Fe (mol %) 1 18.5 15.3 7.3 48.3 223.5 22.3 10.5 36.3 3 31.2 21.6 7.1 42.3 4 23.5 25.3 9.3 37.5 5 36.316.2 8.8 44.4 6 37.5 23.2 10.5 33.8 7 24.5 25.3 6.3 39.6 8 26.5 23.412.3 41.6 9 21.1 18.8 8.6 46.3 10  23.6 20.3 9.1 43.2 Average Value26.62 21.17 8.98 41.33 Standard 6.02 3.31 1.72 4.32 Deviation

TABLE 5 Additive Content Amount and Maximum Value of Standard Deviationfor Cathode configured from Sample No. 1 to No. 10 of(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ Standard Deviation AdditiveContent Sample A Site B Site Amount (ppm) No. La Sr Co Fe P Cr B 1 6.023.31 1.72 4.32 40 400 30 2 2.98 4.08 1.21 1.68 35 300 20 3 10.4  9.122.68 3.78 50 500 50 4 1.36 0.92 0.55 0.45 40 250 20 5 7.88 14.1  5.213.12 70 800 80 6 11.3  6.45 3.01 4.85 60 630 60 7 0.03 0.03 0.12 0.08 2020 3 8 0.32 0.48 0.06 0.08 30 100 5 9 1.25 0.98 0.72 0.45 45 460 50 100.25 0.33 0.05 0.09 20 60 10

TABLE 6 Evaluation Result of Deterioration Rate and Maximum Value ofStandard Deviation for Cathode configured from Sample No. 1 to No. 10 of(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ Maximum Maximum Value ValueStandard Standard Deterioration Sample Deviation at Deviation at B RateEvaluation No. A site site (%/1000 hr) Result 1 6.02 4.32 0.76 Good 24.08 1.68 0.63 Good 3 10.4 3.78 0.95 Good 4 1.36 0.55 0.65 Good 5 14.15.21 1.85 Poor 6 11.3 4.85 1.52 Poor 7 0.03 0.12 0.3 Good 8 0.48 0.080.52 Good 9 1.25 0.72 0.87 Good 10 0.33 0.09 0.45 Good

As illustrated in FIG. 4 to FIG. 5 and Table 1 to Table 3, thedeterioration rate was suppressed to a small value for samples No. 1 toNo. 4, and No. 7 to No. 10. These samples exhibit a standard deviation(scattering) for the atomic percentage of elements at the A site of lessthan 11.5, more specifically, the value was no more than 10.3. Thestandard deviation for the atomic percentage of elements at the B sitewas no more than 3.99.

As shown by Table 4 to Table 6, the deterioration rate is reduced by alarge extent at the cathode configured from samples No. 1 to No. 4 andNo. 7 to No. 10. In these cathodes, the standard deviation of the atomicpercentage of each element at the A site is less than 11.3, and morespecifically, is less than or equal to 10.4. The standard deviation ofthe atomic percentage of each element at the B site is less than orequal to 4.32.

In samples No. 5 and No. 6 which exhibited a large deterioration rate,the standard deviation for the atomic percentage of elements at the Asite was at least 11.5, and the standard deviation for the atomicpercentage of elements at the B site was at least 4.88.

In cathodes configured by samples No. 5 to No. 6 in which thedeterioration rate was increased, the standard deviation of the atomicpercentage of each element at the A site is at least 11.3. The standarddeviation of the atomic percentage of each element at the B site is atleast 4.85.

C-2 No. 11 to No. 16: (La_(0.8)Sr_(0.2))FeO₃

In relation to the samples No. 11 to No. 16, the measurement resultsusing the concentration of No. 11 sample as an example, and the resultsof the calculation of the average value and the standard deviation areshown in Table 7. Table 8 shows the maximum value of the standarddeviation for the atomic percentage of each element in relation tosamples No. 11 to No. 16. The maximum value of the standard deviation atthe A site and the maximum value of the standard deviation at the B siteare underlined in relation to each sample. Table 9 shows the maximumvalue of the standard deviation at the A site and the maximum value ofthe standard deviation at the B site shown in Table 8, the voltage droprate (deterioration rate) per 1000 hours, and the evaluation resultsbased on the voltage drop rate for samples No. 11 to No. 16.

Table 10 shows the measurement results for the concentration and thecalculation results for the average value and standard deviation at thesectional surface of the cathode according to sample No. 11 of thesamples No. 11 to No. 16. Table 11 shows the maximum value of thestandard deviation value of the atomic percentage of each element forthe cathode according to No. 11 to No. 16. In Table 11, an underline isapplied to the maximum value for the standard deviation value at the Asite and the maximum value for the standard deviation value at the Bsite. Table 12 shows the maximum value of the standard deviation at theA site and the maximum value of the standard deviation at the B siteshown in Table 11, the voltage drop rate (deterioration rate) per 1000hours, and the evaluation results based on the voltage drop rate for thecathode according to samples No. 11 to No. 16.

TABLE 7 Concentration Analysis Results for 10 Spots in Sample No. 11 of(La_(0.8)Sr_(0.2))FeO₃ Analysis Spot La (mol %) Sr (mol %) Fe (mol %) 136.4 8.8 54.8 2 35.9 9.1 55.0 3 30.5 11.4 58.1 4 36.1 8.8 55.1 5 41.86.5 51.7 6 36.9 8.5 54.6 7 49.7 6.1 44.2 8 28.2 11.1 60.7 9 36.8 8.754.5 10  42.0 6.6 51.4 Average Value 37.43 8.56 54.01 Standard 5.74 1.714.16 Deviation

TABLE 8 Maximum Value for Standard Deviation and Additive Content Amountfor Samples No. 11 to No. 16 of (La_(0.8)Sr_(0.2))FeO₃ StandardDeviation Additive content Synthesis A site B site amount (ppm) SampleNo. Method La Sr Fe P Cr B 11 Solid phase 5.74 1.71 4.16 20 100 10method 12 Solid phase 4.28 2.95 3.25 30 300 20 method 13 Solid phase7.91 2.77 3.68 50 500 50 method 14 Solid phase 10.95  2.65 4.98 60 55070 method 15 Liquid phase 1.04 1.73 0.65 20 80 10 method 16 Liquid phase0.43 0.09 0.21 10 30 5 method

TABLE 9 Evaluation Result for Deterioration Rate and Maximum Value ofStandard Deviation in Samples No. 11 to No. 16 of (La_(0.8)Sr_(0.2))FeO₃Maximum Value Maximum Value Standard Standard Deterioration SampleDeviation at Deviation at B Rate Evaluation No. A site site (%/1000 hr)Result 11 5.74 4.16 0.34 Good 12 4.28 3.25 0.42 Good 13 7.91 3.68 0.55Good 14 10.95 4.98 1.23 Poor 15 1.73 0.65 0.32 Good 16 0.43 0.21 0.22Good

TABLE 10 Concentration Analysis Result for 10 Spots on Cathodeconfigured from Sample No. 11 of (La_(0.8)Sr_(0.2)) FeO₃ Analysis SpotLa (mol %) Sr (mol %) Fe (mol %) 1 39.1 9.3 58.6 2 45.3 9.8 46.9 3 33.311.3 51.2 4 38.1 8.6 44.4 5 42.1 12.1 48.9 6 36.9 7.9 55.8 7 44.4 7.646.3 8 41.2 8.7 51.2 9 39.6 10.3 52.6 10  33.8 11.3 51.8 Average Value39.38 9.69 50.77 Standard 3.83 1.46 4.13 Deviation

TABLE 11 Additive Content Amount and Maximum Value of Standard Deviationfor Cathode configured from Sample No. 11 to No. 16 of(La_(0.8)Sr_(0.2)) FeO₃ Standard Deviation Additive Content Sample ASite B Site Amount (ppm) No. La Sr Fe P Cr B 11 3.83 1.46 4.13 20 100 1012 4.44 3.02 3.33 30 300 20 13 8.15 2.55 3.58 50 500 50 14 11.2  2.985.11 60 550 70 15 1.25 1.89 0.88 20 80 10 16 0.59 0.12 0.25 10 30 5

TABLE 12 Evaluation Result of Deterioration Rate and Maximum Value ofStandard Deviation for Cathode configured from Sample No. 11 to No. 16of (La_(0.8)Sr_(0.2)) FeO₃ Maximum Value Maximum Value Standard StandardDeterioration Sample Deviation at Deviation at B Rate Evaluation No. Asite site (%/1000 hr) Result 11 3.83 4.13 0.34 Good 12 4.44 3.33 0.42Good 13 8.15 3.58 0.55 Good 14 11.2 5.11 1.23 Poor 15 1.89 0.88 0.32Good 16 0.59 0.25 0.22 Good

As illustrated in Table 7 to Table 9, the deterioration rate wassuppressed to a small value for samples No. 11 to No. 13, No. 15 and No.16. These samples exhibit a standard deviation (scattering) for theatomic percentage of elements at the A site of no more than 7.91, andthe standard deviation for the atomic percentage of elements at the Bsite was no more than 4.16.

As shown by Table 10 to Table 12, the deterioration rate is reduced by alarge extent on the cathode configured from samples No. 11 to No. 13 andNo. 15 to No. 16. In these cathodes, the standard deviation of theatomic percentage of each element at the A site is less than 11.2, andmore specifically, is less than or equal to 8.15. The standard deviationof the atomic percentage of each element at the B site is less than orequal to 4.13.

In sample No. 14 which exhibited a large deterioration rate, thestandard deviation for the atomic percentage of elements at the A sitewas at least 10.95. In sample No. 14, the standard deviation for theatomic percentage of elements at the B site was comparatively large at4.98.

In cathodes configured by sample No. 14 in which the deterioration ratewas increased, the standard deviation of the atomic percentage of eachelement at the A site is 11.2, and the standard deviation of the atomicpercentage of each element at the B site is 5.11.

C-3 No. 17 to No. 22: La(Ni_(0.6)Fe_(0.4))O₃

In relation to the samples No. 17 to No. 22, the measurement resultsusing the concentration of No. 17 sample as an example, and the resultsof the calculation of the average value and the standard deviation areshown in Table 13. Table 14 shows the maximum value of the standarddeviation for the atomic percentage of each element in relation tosamples No. 17 to No. 22. The maximum value of the standard deviation atthe A site and the maximum value of the standard deviation at the B siteare underlined in relation to each sample. Table 15 shows the maximumvalue of the standard deviation at the A site and the maximum value ofthe standard deviation at the B site shown in Table 14, the voltage droprate (deterioration rate) per 1000 hours, and the evaluation resultsbased on the voltage drop rate for samples No. 17 to No. 22.

Table 16 shows the measurement results for the concentration and thecalculation results for the average value and standard deviation at thesectional surface of the cathode according to sample No. 17 of thesamples No. 17 to No. 22. Table 17 shows the maximum value of thestandard deviation value of the atomic percentage of each element forthe cathode according to No. 17 to No. 22. In Table 17, an underline isapplied to the maximum value for the standard deviation value at the Asite and the maximum value for the standard deviation value at the Bsite. Table 18 shows the maximum value of the standard deviation at theA site and the maximum value of the standard deviation at the B siteshown in Table 17, the voltage drop rate (deterioration rate) per 1000hours, and the evaluation results based on the voltage drop rate for thecathode according to samples No. 17 to No. 22.

TABLE 13 Concentration Analysis Results for 10 Spots in Sample No. 17 ofLa(Ni_(0.6)Fe_(0.4))O₃ Analysis Point La (mol %) Ni (mol %) Fe (mol %) 140.3 28.7 31.0 2 37.4 33.9 28.7 3 48.7 31.5 19.8 4 58.1 25.4 16.5 5 41.832.0 26.2 6 40.9 34.8 24.3 7 42.1 29.9 28.0 8 59.2 23.9 16.9 9 35.7 36.427.9 10  47.9 28.9 23.2 Average Value 45.21 30.54 24.25 StandardDeviation 7.72 3.79 4.81

TABLE 14 Maximum Value for Standard Deviation and Additive ContentAmount for Samples No. 17 to No. 22 of La(Ni_(0.6)Fe_(0.4))O₃ StandardDeviation Additive content Synthesis A site B site amount (ppm) SampleNo. Method La Ni Fe P Cr B 17 Solid phase 7.72 3.79 4.81 40 400 50method 18 Solid phase 10.5  6.35 1.23 60 600 60 method 19 Solid phase5.23 4.35 2.35 50 500 30 method 20 Solid phase 3.52 4.23 1.85 30 250 20method 21 Liquid phase 1.35 1.23 0.85 20 100 10 method 22 Liquid phase0.35 0.33 0.36 10 50 5 method

TABLE 15 Evaluation Result for Deterioration Rate and Maximum Value ofStandard Deviation in Samples No. 17 to No. 22 of La(Ni_(0.6)Fe_(0.4))O₃Maximum Value Maximum Value Standard Standard Deterioration SampleDeviation Deviation at B Rate Evaluation No. at A site site (%/1000 hr)Result 17 7.72 4.81 0.78 Good 18 10.5 6.35 1.65 Poor 19 5.23 4.35 0.75Good 20 3.52 4.23 0.68 Good 21 1.35 1.23 0.46 Good 22 0.35 0.36 0.45Good

TABLE 16 Concentration Analysis Result for 10 Spots on Cathodeconfigured from Sample No. 17 of La(Ni_(0.6)Fe_(0.4))O₃ Analysis Spot La(mol %) Ni (mol %) Fe (mol %) 1 41.6 31.2 28.6 2 33.6 36.3 19.6 3 46.330.3 22.2 4 41.3 22.2 26.5 5 56.5 23.6 28.6 6 44.3 38.6 18.6 7 38.5 31.223.6 8 55.1 33.3 27.4 9 46.5 25.6 21.6 10  42.5 32.5 20.6 Average Value44.62 30.48 23.73 Standard 6.64 5.03 3.59 Deviation

TABLE 17 Additive Content Amount and Maximum Value of Standard Deviationfor Cathode configured from Sample No. 17 to No. 22 ofLa(Ni_(0.6)Fe_(0.4))O₃ Standard Deviation Additive Content Sample A SiteB Site Amount (ppm) No. La Ni Fe P Cr B 17 6.64 5.03 3.59 40 400 50 1810.8  6.26 1.65 60 600 60 19 4.89 4.12 2.12 50 500 30 20 3.02 3.99 2.0130 250 20 21 1.89 1.65 1.13 20 100 10 22 0.38 0.42 0.45 10 50 5

TABLE 18 Evaluation Result of Deterioration Rate and Maximum Value ofStandard Deviation for Cathode configured from Sample No. 17 to No. 22of La(Ni_(0.6)Fe_(0.4))O₃ Maximum Value Maximum Value Standard StandardDeterioration Sample Deviation at Deviation at B Rate Evaluation No. Asite site (%/1000 hr) Result 17 6.64 5.03 0.78 Good 18 10.8 6.26 1.65Poor 19 4.89 4.12 0.75 Good 20 3.02 3.99 0.68 Good 21 1.89 1.65 0.46Good 22 0.38 0.45 0.45 Good

As illustrated in Table 13 to Table 15, the deterioration rate wassuppressed to a small value for samples No. 17, No. 19 to No. 22. Thesesamples exhibit a standard deviation (scattering) for the atomicpercentage of elements at the A site of no more than 7.72. These samplesexhibit the standard deviation for the atomic percentage of elements atthe B site was no more than 4.81.

As shown by Table 16 to Table 18, the deterioration rate is reduced by alarge extent on the cathode configured from samples No. 17 and No. 19 toNo. 22. In these cathodes, the standard deviation of the atomicpercentage of each element at the A site is less than 10.8, and morespecifically, is less than or equal to 6.64. The standard deviation ofthe atomic percentage of each element at the B site is less than orequal to 5.03.

On the other hand, the standard deviation for the atomic percentage ofelements at the A site in sample No. 18 which exhibited a largedeterioration rate was relatively large at 10.5, and the standarddeviation for the atomic percentage of elements at the B site was alsocomparatively large at 6.35.

In cathodes configured by sample No. 18 in which the deterioration ratewas increased, the standard deviation of the atomic percentage of eachelement at the A site is 10.8, and the standard deviation of the atomicpercentage of each element at the B site is 6.26.

C-4 No. 23 to No. 28: (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃

Table 10 shows the measurement results for the voltage drop rate(deterioration rate) per 1000 hours and the concentration of theadditive (P, Cr and B) for Samples No. 23 to No. 28.

TABLE 19 Additive content Deterioration Sample Synthesis amount (ppm)Rate Evaluation No. Method P Cr B (%/1000 hr) Result 23 Solid phase 60530 75 1.66 Poor (X) method 24 Liquid phase 50 500 50 0.65 Good (◯)method 25 Solid phase 40 250 25 0.56 Good (◯) method 26 Liquid phase 30100 10 0.38 Good (⊚) method 27 Liquid phase 15  65  5 0.23 Good (⊚)method 28 Liquid phase less less less 1.23 Poor (X) method than than 1than 1 1

As illustrated in Table 19, the deterioration rate was not suppressed toa small value in sample No. 28. Therefore, it is determined thataddition of at least 1 ppm of all of P, Cr and B to the cathode materialis preferred. In the same manner, it is determined that the addition ofall of P, Cr and B at least 1 ppm to the cathode is preferred.

The deterioration rate was not suppressed to a small value in relationto sample No. 23. Therefore it was confirmed that the preferred contentamount in the electrode material of P is no more than 50 ppm, thepreferred content amount in the cathode material of Cr is no more than500 ppm, and the preferred content amount in the electrode material of Bis no more than 50 ppm. In the same manner, it is confirmed that acontent amount of P in the cathode of less than or equal to 50 ppm, acontent amount of Cr of less than or equal to 500 ppm, and a contentamount of B of less than or equal to 50 ppm are preferred.

A comparison of No. 24, 25 and No. 26, 27 enables confirmation that thepreferred content amount in the electrode material of P is no more than30 ppm, the preferred content amount in the cathode material of Cr is nomore than 100 ppm, and the preferred content amount in the electrodematerial of B is no more than 10 ppm. In the same manner, it isconfirmed that a content amount of P in the cathode of less than orequal to 30 ppm, a content amount of Cr of less than or equal to 100ppm, and a content amount of B of less than or equal to 10 ppm are morepreferred.

C-5 Summary

From the above results, the deterioration of the cathode can besuppressed by a relatively uniform configuration in the distribution ofatoms (small standard deviation) in the cathode and the cathodematerial.

It was confirmed that the content amount of additives (P, Cr and B)contained in the cathode and the cathode material results in a smallstandard deviation when 1 ppm≦P≦50 ppm, 1 ppm≦Cr≦500 ppm and 1 ppm≦B≦50ppm.

From the point of view of a stable microstructure in a porous electrode,the content amount of additives (P, Cr and B) contained in the cathodeand the cathode material has been confirmed to be 1 ppm≦P≦30 ppm, 1ppm≦Cr≦100 ppm and 1 ppm≦B≦10 ppm. These results demonstrate an effectof strengthening of the backbone of a porous electrode by addition of amicroscopic amount of the additives.

Wet assay (ICP analysis) was used to confirm that the macro compositionof each sample coincides with the well-formed composition of the rawmaterials.

The relationship between the atomic distribution and the deteriorationof the cathode is purported to be as follows.

Even when the overall composition of the powdered cathode materialcoincides with the well-formed composition, if the location(distribution) of respective elements is not uniform when themicro-portions are observed, the composition of those portions deviatesfrom the overall composition. Catalytic activity and conductivity is lowin such portions, and thereby a cathodic function during powergeneration operations is low. When operating as a fuel cell, currentflow tends to avoid such inactive portions, and thereby the currentdensity is increased in the periphery of such portions. As the result,the deterioration of such peripheral portions is accelerated.

Although the scattering of the atomic percentage was calculated in eachtable by use of a disintegrated product, since the spot diameter duringanalysis for a powdered material is smaller than the diameter of adisintegrated product, it was confirmed for all materials that there isno difference in relation to the atomic distribution configuration(scattering) from a disintegrated product.

The technique disclosed herein is useful in relation to a solid oxidefuel cell to thereby suppress deterioration of the cathode.

1. A solid oxide fuel cell comprising: a cathode including a complexoxide having a perovskite structure expressed by the general formulaABO₃; an anode; and a solid electrolyte layer disposed between thecathode and the anode, a standard deviation value for an atomicpercentage of respective elements at the A site measured using energydispersive X-ray spectroscopy at 10 spots in a single field on asectional surface of the cathode being no more than 10.4.
 2. The solidoxide fuel cell according to claim 1, wherein a standard deviation valuefor the atomic percentage of respective elements at the B site measuredusing energy dispersive X-ray spectroscopy at 10 spots in a single fieldis less than or equal to 5.03.
 3. The solid oxide fuel cell according toclaim 1, wherein the A site is selected from the group including La andSr.
 4. The solid oxide fuel cell according to claim 1, wherein at leastone atom of Co and Fe is included at the B site.
 5. The solid oxide fuelcell according to claim 1, wherein the complex oxide is (La, Sr)(Co,Fe)O₃, (La, Sr)FeO₃, (La, Sr)CoO₃, or La(Ni, Fe)O₃.
 6. The solid oxidefuel cell according to claim 1, wherein the single field is a rangeobserved by an electron microscope with a magnification of 100 times to5000 times.
 7. The solid oxide fuel cell according to claim 1, wherein asize of the respective 10 spots is no more than 1 micrometer.
 8. Thesolid oxide fuel cell according to claim 1, wherein the position of the10 spots is selected from the single field on the basis of theconcentration level in 10 stages determined in response to adistribution of the atomic percentage in the single field.
 9. The solidoxide fuel cell according to claim 8, wherein the concentration level ofthe 10 stages is set across an entire range of the distribution of theatomic percentage in the single field.
 10. A solid oxide fuel cellcomprising: a cathode including a complex oxide having a perovskitestructure expressed by the general formula ABO₃; an anode; and a solidelectrolyte layer that is disposed between the cathode and the anode, astandard deviation value for the atomic percentage of respectiveelements at the B site measured using energy dispersive X-rayspectroscopy at 10 spots in a single field on a sectional surface of thecathode being less than or equal to 5.03.